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Lithium Ion Batteries
George T. K. Fey
Department of Chemical and Materials Engineering
National Central University
Chung-Li, Taiwan ROC
Due to the rapid increase in the use of portable computers, mobile phones, video
cameras, electric vehicles, etc., there is an increasing demand for larger capacity,
smaller size, lighter weight and lower priced rechargeable batteries. Lithium-ion
batteries (LIBs) have become the predominant battery technology for handheld
electronic applications in the recent decade due to their high energy, high voltage,
good cycle life and excellent storage characteristics. LIBs have an energy density that
is more than double that of NiCd and its load current is reasonably high. The LIB also
acts similarly to NiCd in terms of discharge characteristics and has a relatively low
Sony introduced LIBs to the marketplace in June 1991 and may potentially
dominate the small sealed rechargeable battery market for some time to come. In 2002
the production of small lithium-ion batteries was about 752 million cells, worldwide.
The market had an overall growth rate of about 15%. Present LIBs range in energy
storage capability from 200 to 250 Wh/l and from 100 to 125 Wh/kg. LIBs have
proven to be extremely safe with many hundreds of millions of cells shipped with
very few reported incidents.
Lithium has been the first metal of choice for batteries because it is the lightest
of all metals. It has the greatest electrochemical potential and provides the largest energy content. Rechargeable lithium batteries provide high voltage, excellent capacity and extraordinary energy density. G.N. Lewis pioneered lithium battery research back in 1912 but active research did not begin until the 1950s when it was noticed that Li-metal was stable in a number of non-aqueous electrolytes such as fused salts, liquid SO2 or organic electrolytes such as LiClO4 in propylene carbonate . The commercialization of primary lithium batteries followed relatively quickly in the late 1960s and 1970s. Some of the primary lithium batteries that are still being manufactured today are Li/SO2 cells , Li/MnO2 cells , Li/(CFx)n cells , etc. These primary cells have been used mainly for watches, calculators, medical implants and military applications, with Li/MnO2 being dominant in the consumer market.
Not surprisingly, the development of rechargeable lithium batteries was far from
easy and much slower. Early success started with the Exxon Li/TiS2 system  in the mid 1970s as a coin cell for electronic watches. Since then, large numbers of
secondary systems with different cathode materials, different lithium metal or lithium compound based anodes and electrolytes have been studied and developed (Slide xx). For the sake of safety, these systems were manufactured only as coin cells in Japan. The development of secondary cells larger than coin cells began in the early 1980s by two Canadian companies, Ballard Research Inc. (now as Ballard Power System, Inc.) and Moli Energy, Ltd., both located in Vancouver, B.C. The former attempted the Li/SO2 system and the latter developed the Li/MoS2 system. Although Li/SO2 cells can be cycled more than one hundred cycles in these inorganic electrolytes, research in this field was discontinued because they could not be used for consumer applications and there were safety concerns regarding cell venting. However, Moli Energy became the first manufacturer of commercial secondary lithium batteries in the world in the late 1980s. Unfortunately, in the summer of 1989, NTT of Japan recalled all batteries for its cellular telephone that used Moli Energy’s Li/MoS2 secondary cells because of incidents involving cells that caught fire during assembly. This setback eventually led to the bankruptcy of Moli Energy and also brought worldwide attention to the safety risks associated with primary and secondary lithium cells.
Since lithium metal is naturally unstable, especially during charging, the focus
then shifted to non-metallic lithium batteries using carbon as an anode material and
LiCoO2 as a cathode material. The new lithium ion system using carbon as an anode
has a lower energy density than the old lithium metal system, but it is safer, provided
that certain precautions are taken during charging and discharging. Sony was the first
to commercialize the lithium ion battery in 1991 and still remains the largest supplier
of this type of battery. Their key contributions are: 1) identifying the right
combination of materials, 2) incorporating automated manufacturing for mass
production, 3) implementing a number of safety measures such as a special “smart
charger”, 4) discovering a porous polymer to prevent overheating. The lithium ion
battery is the rising star of small sealed secondary batteries for the new century. Cell Electrochemistry
When LIBs are first charged, lithium ions are transferred from the layers of the
lithium cobaltite to graphite. The initial charging reaction proceeds as:
LiCoO2 + 6C <
-- ---------- Li1-xCoO2 + C6Lix .
During the first charge, graphite surface is covered by a passivation film, consuming some of the inserted lithium and preventing further solvent reduction. Usually, the first charge efficiency is about 85 to 95%. Subsequent charge and discharge reactions
are then based on the motion of lithium ions between the anode and cathode, approximately half of the intercalated lithium may be removed reversibly, as shown: .
Li0.55CoO2 + 0.45Li+ + 0.45e- <------- LiCoO2 (123 mAh/g)
Li0.35NiO2 + 0.5Li+ + 0.5e- <------- Li0.85NiO2 (135 mAh/g)
The solid state chemistry of the LiNiO2 cathode is more complex than that of LiCoO2
and the fully lithiated compound is not stable during electrochemical cycling. In order
to circumvent this problem, doping with an inert metal ion and forming substitutional
oxides on the cathode surface may improve the electrode stability and cell cyclability.
A typical example for the electrode reaction of LiNi1-yCoyO2 cycling between 4.1 to
2.7 V at room temperature is given as below:
LiNi(1-y-z)CoyAlzO2 ------------------- Li0.35Ni(1-y-z)CoyAlzO2 + 0.65Li+ + 0.65e- (A)
Li0.35Ni(1-y-z)CoyAlzO2 + 0.5Li+ + 0.5e- ----------- Li0.85Ni(1-y-z)CoyAlzO2 (B)
The capacity in the electrode reaction (A) is 180 mAh/g while that in (B) is 140
mAh/g. However, on discharge at higher temperature than ambient (e.g. 45/60 ℃)
almost all Li can be reinserted during discharge, resulting on increased capacity to
170 mAh/g, as shown below.
Li0.35Ni(1-y-z)CoyAlzO2 + 0.6Li+ + 0.6e- ----------- Li0.95Ni(1-y-z)CoyAlzO2 (C) System Description
The lithium battery without lithium metal is referred to as the lithium-ion battery
(LIB) or Swing battery. During charge and discharge, the lithium ion rocks back and forth between the anode and cathode and no metallic lithium is plated. This cell system is also referred to as the rocking-chair battery. Both rocking-chair battery and lithium-ion battery are commonly used in the battery field. The first term is still used by many academics and is found throughout the history of lithium battery development. However, the latter term was adopted by the Japanese after Sony’s commercialization in 1991. It was more practical and reflected the reality that Japanese manufacturers dominated the industry.
A major challenge is to find a safer material in which to store and transport
lithium ions in the battery. Carbonaceous materials are super candidates. They are cheap, safe and do not pollute the environment. Graphite itself is a good host for lithium ions, accepting intercalation up to a composition approaching C6Li (372 mAh/g), at a voltage of zero to 1 V with respect to a lithium reference electrode.
At present, all commercially available LIBs use carbon as the anode material and
layered transition metal oxides LiMO2 (where M = Co, Ni or Mn) – examples include LiCoO2 (lithium cobaltite) and LiNiO2 (lithium nickelite) – and the spinel material LiMn2O4 as the active material of the cathode. Since LiCoO2 offers superior reversibility, discharge capacity, and charge/discharge efficiency, it is the dominant cathode material of choice for small cells used in portable electronics.
There are three major kinds of carbon available for LIBs:
Graphite types – highly structured Coke types – less structured but easily transformed into graphite by heating Non-graphitizable (hard) carbon types – highly disordered.
Since non-graphitizable (hard) carbonaceous materials with high irreversible capacity are not ready for commercialization, the first two types of Li-ion electrode have been developed. The coke version was developed by Sony and the graphite version was adopted by most other manufacturers such as Sanyo, Matsushita (Panasonic) and Japan Storage Battery Co., Ltd. (JSB or GS).
The graphite electrode delivers a flatter discharge voltage curve than the coke
electrode and offers a sharp knee bend, followed by a rapid voltage drop before the voltage cutoff point as can be seen in Slide xx which illustrates discharge characteristics of LIBs with coke and graphite electrodes. Because of its discharge profile, the graphite LIB only needs to be discharged to 3.0V per cell, but the Sony LIB needs to be discharged to 2.5V in order to achieve maximum capacity. The higher end-of-discharge voltage is a major advantage because useful energy is concentrated within a narrow upper voltage range, which allows for simpler equipment design. The graphite version is also able to deliver a higher discharge current and stays cooler during charge and discharge.
As LIBs are charged and discharged, Li-ions are transported between their
carbon-based anode and their LiCoO2-based cathode, with electrons exchanged as a result of Li-ion insertion (doping) and of Li-ion extraction (undoping). During charging, the cathode is undoped (i.e. Li-ions are removed) and the anode is doped
(i.e. Li-ions are inserted). The schematic of the charge/discharge process is illustrated
in Slide. xx.
When cycling LIBs, it is critical to follow the control of the top-of-charge voltage (4.1
V for LiNiO2 and 4.2 V for LiCoO2). Failure to do so results in decomposition of the
cathode and oxygen gas, Co3O4, or LiNi2O4 is produced. The cobalt, nickel and
manganese oxides liberate oxygen at higher temperatures and can constitute a safety
hazard. If the electrolyte solvents exceed their flash points, they can burn inside the
cell. In addition, over-discharge must also be avoided and it is normal to have a
limiting cut-off voltage on discharge of about 2.7 V. For safety and longevity
reasons, each LIB pack must be equipped with a specially designed charger
incorporating voltage, current and temperature control. With these precautions in
place, the possibility of metallic lithium plating occurring due to overcharge and
over-discharge is virtually eliminated. Features
The LIB technology offers the highest energy densities by weight of all the
commercial rechargeable battery technologies with the following features and
benefits. High Energy Density
LIBs weigh around half that of a NiCd or NiMH cell of the same capacity. In
addition, LIBs are 40 to 50% volumetrically smaller than NiCd cells, and 20 to 30 % smaller than NiMH cells.
The chemical bond of lithium to the electrode material is stronger, leading to a
significantly higher charging voltage necessary to break this bond. The average
voltage of a LIB (3.6 to 3.7 V) is equivalent to three NiCd or NiMH cells (each 1.2 V).
This means that one cell is all that is required for many of today’s portable electronic
devices (MP3 players, mobile phones, etc.). High Drain Capacity
LIBs can typically be discharged at rates up to 1.5 C continuous. High capacity,
higher drain multi-cell packs are achieved by connecting multiple cells in parallel –
something which is not easily done when using NiCd or NiMH cells.
LIBs are free from metals such as mercury, lead and cadmium – they meet the
requirements of the Toxic Chemicals Directive 91/157/EEC. Lithium Metal Free
Unlike primary lithium metal cells, rechargeable LIBs do not contain lithium in its
metallic state – making them less restrictive to transport. Long Cycle Life
When charged and discharged under normal conditions, the life of a LIB is typically
between 300 and 500 cycles. Allow Flexible User Patterns
LIBs are free from the so called memory effect which can be seen to reduce the
capacity of NiCd cells after numerous shallow charge/discharge cycles. This makes
ownership easier for the end user. Fast Charge Capable
LIBs can be fast charged with around 70-80% of typical capacity being available after
around 1 hour when charged at 1C. Wide Environmental Operation Range
LIBs can typically be charged between 0 and 45℃, and discharged between –20 and
+60℃. Special cells are available for operation outside this range allowing discharge
operation between –40 and +70℃. References
1. R. Jasinski, High Energy Batteries, Plenum Press, N. Y. 1967.
2. A. V. Fraioly, W. A. Barber and A. M. Feldman, U.S. Patent 3,551,205 (1970).
3. H. Ikeda, T. Saito and H. Tamura, in: Proc. Manganese Dioxide Symposium,
Vol. 1, eds. A. Kozawa and R. H. Brodd (I. C. Sample Office, Cleveland, OH,
4. M. Fukuda and T. Iijima, in Power Sources, Vol. 5, ed. D. H. Collins
(Academic Press, London, 1975) p.713.
5. M. S. Whittingham, Science 192 (1976) 1126.
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